Existing water filter cartridges have an elongated housing for filter media with a neck that fits into a manifold in the appliance. The neck of the filter cartridge or the top part of the filter cartridge typically has a bayonet mount with inclined (cam) ends that rotatably engage a mating flange in the manifold so that rotating the filter cartridge locks the cartridge into position during use. When the manifold allows pressurized water to flow into and through the filter cartridge the water exerts an axial force on the cartridge that wants to push the filter cartridge out of the manifold. The bayonet mount resists this ejection pressure and prevents the water pressure in the manifold from pushing the filter cartridge out of the manifold.
Sometimes the filter cartridge splits open because the line pressure in the manifold is at too high of a pressure or because repeated pressure variations (water hammer) gradually weaken the filter cartridge housing, causing it to break. High line pressures arise because the municipal water line often carries water at pressures of 60-120 psi, with a home pressure regulator typically being located between the municipal water line and the home in which the appliance is located for a more typical line pressure of about 60-80 psi. These home pressure regulators typically regulate the pressure in residential water lines to about 60 psi, but the selected pressure is adjustable. These home pressure regulators wear and may cause excessive line pressure damaging to appliance water filters, and sufficiently damaging that the housings on appliance water filters may rupture or leak.
Moreover, even at 60 psi, valves associated with various residential and office items that use water, such as sprinklers, toilets, washers, faucets, showers, bathtubs, water heaters and outdoor hose bibs may have valves configured to operate various different pressures so that the opening and especially the closing of these valves causes a sudden back pressure in the residential water line, resulting in water hammer. The pressures from water hammer can be very high, and can occur with high frequency. Water hammer may occur with sufficient frequency and magnitude that the water filter cartridges rupture or that the home pressure regulator is damaged and allows increased line pressure to the home.
When a water filter cartridge ruptures or leaks, water can flood the surrounding area, causing damage to the affected area commensurate with the volume and duration of the leak and the location of the lead. The result can be very large damage claims by the homeowner. Since there is currently no reliable way to show the rupture of a water filter cartridge was caused by too much line pressure from the appliance's manifold, the cartridge manufacturer may sometimes be held liable for the water damage when the failure was not caused by the filter cartridge. To help avoid such ruptures, leaks and water damage, filter cartridges are tested to at 300 psi and sometimes up to 500 psi, even though the cartridge is rated at 60 psi for operational uses. Typically, the rated operating pressure is qualification tested to three times that rated pressure. But despite this overpressure testing, cartridge failures still occur. There is thus a need to help determine whether the failure of a water filter arises from overpressure in the water supplied to the filter. There is a further need to help determine whether the failure of a water filter arises from water hammer. There is a further need to help determine whether the failure of a water filter is due to a defect in the filter or something outside the filter. There is a still further need to help determine the source of filter cartridge failures while still allowing the cartridge to be tested using pressures greater than the represented operating pressure at which the filter cartridge is advertised and sold.